A hollow turbine blade 10 as illustrated in FIG. 1A generally includes an airfoil shaped body 12 extending radially between a tip end 14 and a rotor portion 16, extending axially between a leading edge 18 and a trailing edge 20. The turbine blade 10 is mounted to a rotor disk 22 by, for example, a “fir tree” attachment (not shown). A pocket or recess 30 is provided at the tip end 14 of the otherwise solid blade body 12. A creep pin 32 may optionally be provided for use in measuring blade creep. To permit accurate measurements to be made, the creep pin 32 is located close to the tip end 14, and axially where the pocket or recess 30 is widest, i.e. toward the leading edge side of the pocket, to thereby facilitate access by the appropriate measuring tools.
The presence of pocket or recess 30 tends to decrease both the bending and torsional stiffness of the blade 10, or moments of inertia, of the airfoil shaped body 12, which adversely affects the various vibration and bending modes of the blade 10. As a result, a phenomenon known as “second mode bending” can cause a large chord blade to bend, somewhat analogous to flapping like a flag or sail in a breeze. Therefore, the blade chord is usually shortened in region 20′ near the tip end 14, in order to minimize the effect this type of blade trailing edge bending. In essence, the problem is negated by removing or reducing the size of the portion of the blade (i.e. region 20′) most susceptible to second mode bending. Narrowing the blade chord, however, detrimentally affects the turbine performance because a turbine blade with the shortened chord gets less power from combustion gas flow. Therefore, improvements to hollow blades are desirable.